This invention relates generally to an absorption refrigeration unit and, more specifically, to a purge system for use in an absorption unit.
Typically, non-condensable gas that is generated in an absorption refrigeration system is removed by means of an automatic purge system. Non-condensable gases can degrade performance and may be a symptom of a reliability problem, such as corrosion or an air leak.
In some absorption units, solution from the solution pump is passed through an eductor where it is mixed with non-condensables drawn from the absorber. The mixture is then discharged into the condenser. Here, the non-condensables are separated from the solution and are drawn off by means of a second eductor where they are again entrained in solution. The mixture is then discharged into a purge tank where the non-condensables are collected in the top section of the tank and the solution returns to the absorber by means of a return line.
As the tank fills with non-condensables, the solution in the tank is depressed to a point where the tank must be purged. Purging is accomplished by closing a valve in the solution return line and the purge valve in the condenser supply line going to the second eductor. Solution is now forced into the purge tank by the solution pump causing the non-condensables in the purge tank to be compressed. When a sufficient amount of non-condensables have been collected, the exhaust valve in the tank discharge line is opened to allow the non-condensable gas to be bled from the tank into the atmosphere.
As should be evident, in this type of purge system the solution pump must be able to deliver solution to the purge tank at a pressure that is above atmospheric pressure. Many absorption units employ variable speed absorption pumps that oftentimes operate at reduced speeds depending upon the demand on the system, and thus cannot deliver solution at above atmospheric pressure during a purge cycle.
It is, therefore, a primary object of the present invention to improve absorption refrigeration units.
It is a further object of the present invention to improve purge systems employed in absorption refrigeration units.
A still further object of the present invention is to purge non-condensable gases from an absorption refrigeration unit during periods when the solution pump is operating at a reduced speed at which the pumps discharge pressure is below the existing atmospheric pressure.
These and other objects of the present invention are obtained in an absorption refrigeration unit, having an improved system for purging non-condensable gases from the unit during periods when the solution pump is operating with a discharge pressure below atmospheric pressure. An eductor is connected to the discharge side of the solution pump and to the top section of the absorber so that non-condensable gases collected in the absorber are drawn from the absorber and are entrained in the solution. The mixture leaving the eductor is discharged into a purge tank where the non-condensable gases are collected in the top section of the tank over solution that settles in the bottom of the tank. The collected solution is returned to the absorber as the amount of non-condensables increase in the tank. At the start of a purge cycle, the discharge pressure of the solution pump is sensed and when the pressure is below atmospheric pressure, the speed of the pump is increased to bring the discharge pressure up to a desired level that is above atmospheric pressure. A control valve in the return line from the purge tank and a second control valve in the non-condensable input line to the eductor are then closed wherein solution from the pump is forced into the tank to compress the non-condensables collected in the top of the tank. The compressed non-condensables are then exhausted from the tank via an exhaust line.